1. Field of the Invention
The present invention relates to an artificial decapeptide and, more particularly, to an artificial decapeptide for inducing vitellogenesis in fish and its application to aquaculture industry.
2. Description of the Related Art
Marine aquaculture in Taiwan, fish farming in particular, has a long history and been rapid developed in recent decades. Since the advance of aquaculture technique, the fish farming in Taiwan tends to be intensive and industrialized. Accordingly, a significant quantity and quality of broodstock is requested.
The sexual maturation and breeding of fish is involved in a complicated mechanism which has not been well-studied until recent years. Generally, the endocrine system of fish is mainly induced by environmental factors to turn on a hypothalamus-hypophysis-gonad axis responses. In this way, the downstream gonadal developments, including oocyte maturation, vitellogenesis and spawning will be sequentially turned on. Precisely, the hypothalamus will induce the secretion of gonadotropin releasing hormone (GnRH) or gonadotropin inhibiting factor (GnIF), such as dopamine, for catalyzing the synthesis and release of gonadotropin (GtH). The GtH can further phosphorylate protein kinases in ovum or spermatid and induce the steroidogenesis. Finally, the secreted hormone, for example estradiol, leads to vitellogenesis and oocyte maturation, and the ovulation can be sequentially induced by other environmental factors.
In conventional art, GtH, naturally occurred by hypothalamus, are injected into farming broodstock via hypophysation for inducing spawning. However, GtH has big difference among species and have to be genetic expressed rather than chemically synthesized. Hence, the GtH is limited by its higher cost. Otherwise, human chorionic gonadotropin (hCG), commercial LHRHA and domperidome are also used in farming fish. Nevertheless, hCG, commercial LHRHA and domperidome are mainly target to later phase of oocyte development, and which has poor effect on vitellogenesis.
With reference to GB Patent No. 2237571, entitled with “ANALOGUES OF GONADOTROPIN RELEASING HORMONE” GnRH is suggested to play an important in breeding mechanism in vertebrate. Moreover, several naturally occurring vertebrate GnRH has been isolated. However, the conventional invention does not provide a precise application of the GnRH.
Therefore, it is a need of providing an alternative approach for inducing vitellogenesis, ovulation, and spawning of farming fish, in order to improve the conventional technique in aquaculture and establish an effective modulated system for producing high quality and quantity of broodstock.